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Searing hot exoplanet is an unearthly blue

PLANET HD 189733b is blue, and there’s nothing I can do. It doesn’t scan like David Bowie’s original lyric, about Earth, but this alternative is accurate now that an exoplanet’s colour has been measured for the first time.

A gas giant, HD 189733b’s surface is a roasting 844 °C. At 63 light years away, it is too distant for astronomers to separate its light from that of its host star. But using the Hubble Space Telescope, Frédéric Pont of the University of Exeter, UK, and colleagues found a large dip in blue wavelengths when HD 189733b passed behind its star – suggesting that it reflects mainly blue light (Astrophysical Journal Letters, doi.org/m63).

Earth appears as a pale blue dot from space, due to light scattering off the atmosphere, but HD 189733b is darker. Clouds of glassy silica dust make it reflective, while sodium atoms, which absorb red and green, colour it dark blue.

This article appeared in print under the headline “First exoplanet hue is a lovely dark blue”